The anesthetized, paralyzed dog ventilated with an inspired 02 fraction insufficient to support aerobic metabolism at the control level obtained with room air can maintain its arterial blood pressure and its survival, thereby, a variable length of time. This is evidently dependent on the rate of energy deficit accumulation created by the difference in energy production and demand. That rate is assessed by the rate at which excess lactate accumulates in arterial blood. If calorigenic processes which create greater energy demands such as those associated with catecholamine secretion and alkalosis are prevented from occurring during hypoxia, the rate of 02 deficit accumulation also closely approximates that for the energy deficit. With these means of assessing the intensity of energy imbalance, the hypoxia survival preparation will be used as an investigative tool to examine physiologic and functional significance of alterations in the determinant components of tissue 02 delivery. Any change in effective 02 delivery will be reflected as a change in energy imbalance in the situation where energy production is critically limited by 02 availability to the tissues. In this manner, the separate and combined effects of changes in blood 02 carrying capacity, position and shape of the oxyhemoglobin dissociation curve, blood flow and circulating volume will be tested. Addition of other perturbations such as hypoglycemia and alpha-adrenergic blockade are also expected to contribute understanding of the essentials of energy supply in this experimental model. Although immediately beneficial goals will be sought in terms of optimal levels of hematocrit with respect to circulating volume for maximal delivery of 02 to tissues at low levels of 02 availability in the syndrome which might be called "hypoxic shock", the more general goal is a better understanding of the body's "last ditch" defenses when challenged by insufficient 02 supply. Principally, a definitive answer is sought to the question of relative importance for P02 driving pressure and alterations in diffusion distance by opening closed capillaries as ultimate defenses in severe tissue hypoxia. BIBLIOGRAPHIC REFERENCES: Cain, S.M. Oxygen delivery and utilization in dogs with a sublethal dose of cobalt chloride. J. Appl. Physiol. 38:20-25, 1975.